1. Field of the Invention
The present invention relates to electronic siren circuits and more specifically to circuit means for operating a permanent magnet loudspeaker as a siren from a source of chopped d.c. signals. Selectively operable switches connect circuit elements for signal modification.
2. Description of the Prior Art
Prior art electronic circuits such as those shown in U.S. Pat. No. Re. 28,745 issued Mar. 23, 1976, to G. D. Smith and U.S. Pat. No. 3,051,944 issued Aug. 28, 1962, to the same inventor, disclose electronic siren circuits which use an impedance matching transformer between the speaker terminals and the power amplifier. This is standard practice in speaker operation so that during the positive half of an a.c. signal the speaker cone may be pushed in one direction, and during the negative half of the a.c. signal, the speaker cone may be pulled in an opposite direction. D.C. signals to permanent magnet speakers have been considered unsatisfactory because they can push the speaker cone, but not pull it, or vice versa.
Some prior art electronic horns or sirens have included means for altering at least the output sound level. Some have included means for producing a very limited number of different sounds. For example, one commercial model provides for use of up to three of a plurality of about ten available circuit boards. By selective switching, any one of the three circuit boards may be made to control the output sound.